This invention relates to prosthetic devices for interfacing with neural tissue.
Neural tissue can be artificially stimulated and activated by prosthetic devices which pass pulses of electrical current through electrodes on such a device. The passage of current causes changes in electrical potentials across neuronal membranes which can initiate neuron action potentials, which are the means of information transfer in the nervous system. Based on this mechanism, it is possible to input information into the nervous system by coding the information as a sequence of electrical pulses which are relayed to the nervous system via the prosthetic device. In this way, it is possible to provide a variety of artificial sensations including touch, hearing, and vision for a variety of applications. It is also possible to monitor and record neural activity using such a scheme.
One typical application of neural tissue stimulation is in the rehabilitation of the blind. Some forms of blindness involve selective loss of the light sensitive transducers of the retina. Other retinal neurons remain viable, however, and may be activated in the manner described above by placement of a prosthetic electrode device on the inner (toward the vitreous) retinal surface. This placement must be mechanically stable, minimize the distance between the device electrodes and the neurons, and avoid undue compression of the neurons.
The retina is extraordinarily fragile. In particular, retinal neurons are extremely sensitive to pressure; they will die if even a modest intraocular pressure is maintained for a prolonged period of time. Glaucoma, which is one of the leading causes of blindness in the world, can result from a chronic increase of intraocular pressure of only 10 mm Hg. Furthermore, the retina, if it is perforated or pulled, will tend to separate from the underlying epithelium, which will eventually render it functionless. Thus attachment of a conventional prosthetic retinal electrode device is not practical, primarily because of the typically high pressures that such a device would exert on the retina, which would inevitably compromise the retinal neurons.